SoftBank Group Corp. plunged by the most since the early days of the coronavirus pandemic after the company declined to pledge a continuation of buybacks that have propped up its stock.

Shares tumbled as much as 8.7% on Thursday, the most on an intraday basis since March 2020, despite record profit in the March quarter. The company has lost more than ¥6 trillion ($55 billion) in market value in the past three days. Investors are skittish about whether SoftBank will keep buying back its own stock after completing a ¥2.5 trillion allotment for repurchases.

"We believed that SoftBank would follow up its massive buyback with another one. But we are extremely surprised that it did not,” Atul Goyal, senior analyst at Jefferies, wrote in a research note. "Without the buyback, SoftBank stock price is likely to reflect the performance of its listed investments.”